Endovascular cryotreatment catheter

ABSTRACT

An elongated catheter device with a distal balloon assembly is adapted for endovascular insertion. Coolant injected through the device may, in different embodiments, directly cool tissue contacting the balloon, or may cool a separate internal chamber. In the first case, the coolant also inflates the balloon, and spent coolant is returned to the handle via a return passage extending through the body of the catheter. Plural balloons may be provided, wherein a secondary outer balloon surrounds a primary inner balloon, the primary balloon being filled with coolant and acting as the cooling chamber, the secondary balloon being coupled to a vacuum return lumen to serve as a robust leak containment device and thermal insulator around the cooling chamber. Various configurations, such as surface modification of the balloon interface, or placement of particles, coatings, or expandable meshes or coils in the balloon interface, may be employed to achieve this function.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is a continuation-in-part of U.S. patentapplication Ser. No. 09/378,972, filed Aug. 23, 1999.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] n/a

FIELD OF THE INVENTION

[0003] The present invention relates to endovascular catheters, and inparticular, to catheters for cryotreatment of tissue.

BACKGROUND OF THE INVENTION

[0004] The present invention relates to endovascular cryocatheters, suchas angioplasty balloons having a freezing function for treating tissueby extreme cooling contact. These catheters have an elongated bodythrough which a cooling fluid circulates to a tip portion which isadapted to contact and cool tissue. Such a device may include a steeringassembly such as an inextensible pull wire and a flexible tip to whichthe pull wire attaches which may be bent into a curved configuration toaid its navigation through blood vessels to a desired treatment site.When used for angioplasty or the destruction of tissue on the inner wallof a vessel, the catheter generally also has one or more inflatableballoon portions which may serve two functions of displacing blood fromthe treatment site to allow more effective cooling, and physicallydistending the affected vessel to break up accumulations of plaque.

[0005] Endovascular catheters must be of relatively small diameter, andconfigured for insertion along relatively confined pathways to reach anintended ablation site. As such, the cooling fluid must circulatethrough a relatively long and thin body yet apply significant coolingpower in their distal tip. The requirement that coolant be localized inits activity poses constraints on a working device. For example, whenthe catheter must chill tissue to below freezing, the coolant itselfmust obtain a lower temperature to offset the conductive warming effectsof adjacent regions of body tissue. Furthermore, the rate of cooling islimited by the ability to circulate a sufficient mass flow of coolantthrough the active contact region. Since it is a matter of some concernthat proximal, adjacent or unintended tissue sites should not be exposedto harmful cryogenic conditions the flowing coolant must be exposed in alimited region. One approach to cooling uses a phase change refrigerantwhich is provided through the body of the catheter at relatively normalor ambient temperature and attains cooling only upon expansion withinthe tip region. One such device treats or achieves a relatively highrate of heat transfer by using a phase change coolant which is pumped asa high pressure liquid to the tip of the catheter and undergoes itsphase change expanding to a gas in a small chamber located at the tip.The wall of the chamber contacts the adjacent tissue directly to effectconductive cooling or ablation treatment. Other cryocatheters may employgas at high pressure, and achieve cooling via the Joule-Thomson effectat a spray nozzle in a cooling chamber at the distal end of thecatheter.

[0006] In an endovascular catheter as described above, a relatively highcooling power may be obtained. However, the expansion of a phase changeor high pressure coolant exiting from a nozzle within a small cathetertip creates highly turbulent flow conditions. The cooling region of thetip may be implemented as a fairly rigid chamber having highly thermallyconductive wall or section of its wall formed for example by a metalshell. However, if one were to replace such a tip with an inflatableballoon as is commonly used for angioplasty, the size of the chamberwould vary considerably as the balloon is inflated, causing substantialvariations in flow conditions of the fluid entering the tip andsubstantial changes in heat transport across the expanding balloon wall.Both of these factors would result in variations of the cooling powerover the tip. Furthermore, coolant materials suitable for high pressureor phase change refrigeration may pose risks when used within a bloodvessel. Accordingly, there is a need for an improved catheterconstruction for cryogenic angioplasty.

[0007] Another factor which adds complexity to the task of cryocatheterdesign is that the primary mechanism of treatment involves thermalconduction between the catheter and a targeted region of tissue. Thus,not only is the absolute cooling capacity of the catheter important, butthe nature and extent of contact between the cooled region of thecatheter and the adjacent tissue is important. Effective contact mayrequire moving, positioning, anchoring and other mechanisms forpositioning, stabilizing and changing the conformation of the cooledportion of the catheter. Slight changes in orientation may greatly alterthe cooling range or characteristics of the catheter, so that even whenthe changes are predictable or measurable, it may become necessary toprovide positioning mechanisms of high stability or accuracy to assureadequate treatment at the designated sites. Furthermore, it ispreferable that a vessel be occluded to prevent warming by blood flowduring treatment. Beyond that, one must assure that the cooling activityis effective at the surface of the catheter, and further that defects donot cause toxic release of coolant or dangerous release of pressure intothe body.

[0008] Secondary environmental factors, such as the circulation of bloodnear or at the treatment site may also exert a large influence on therate at which therapeutic cooling accrues in the targeted tissue.

[0009] There is therefore a need for improved catheter constructions toocclude blood flow and form a dependable thermal contact with a vesselwall.

[0010] Additionally, the operation of such a device for therapeuticpurposes requires that the coolant be contained within the catheter atall times, lest a leak of coolant enter the body and thereby causesignificant harm. Known catheters which employ inflatable balloons ofteninflate the balloons to relatively high pressures, that exceed theambient pressure in a blood vessel or body lumen. However, to containthe coolant, these catheters generally employ thicker balloons,mechanically rigid cooling chambers, and other similar unitaryconstruction containment mechanisms. These techniques however, lackrobustness, in that if the unitary balloon, cooling chamber, or otherform of containment develops a crack, leak, rupture, or other criticalstructural integrity failure, coolant may quickly flow out of thecatheter.

[0011] There is therefore, for security purposes, a need for improvedcryocatheter constructions to robustly contain coolant flow whencryotreatment is performed.

[0012] Finally, a major challenge for effective cryotreatment is theability to fine tune the pressure and temperature of the coolant flow atthe distal tip of the catheter, so as to controllably apply cooling toadjacent tissue. The cooling power of the device, created through theJoule-Thomson effect and phase change of the coolant as described above,is generally inversely proportional to the resultant coolant pressureachieved after injection into, and during flow through, the coolingchamber or balloon. Thus, in order to maintain the balloon pressure atsafe levels, without exceeding ambient body pressures, the device mustbe operated at relatively lower balloon pressures, which have theundesired effect of raising the cooling power to levels which aredifficult to control and may even harm or damage the target tissue.Therefore, the enhanced cooling power of the device achieved under suchrelatively low operating pressures must be mitigated by providing someform of tunable thermal resistance between the coolant flow and thetarget tissue.

[0013] It is desirable therefore, to provide for an improved cathetersystem which may safely operate at low balloon pressures while thermallyinsulating the target tissue from excessive cooling.

SUMMARY OF THE INVENTION

[0014] In a first embodiment of the present invention, a body insertablecryotreatment catheter is configured with an elongate catheter body, anddistal cooling tip assembly having a cooling chamber surrounded by anexpandable member. The expandable member surrounds the cooling chamberto define an interstitial space therebetween. The interstitial space isin fluid communication with a vacuum source. The cooling chamber may berigid or flexible. A coolant injection lumen is provided in the catheterbody such that the cooling chamber is inflatable by the flow of coolantfrom the injection lumen. Primary and secondary return lumens are influid communication with the cooling chamber and interstitial space,respectively, to: (i) define first and second pathways for the flow ofcoolant, respectively, (ii) contain the coolant flow within the catheterbody in the event of structural failure of the cooling chamber, and(iii) to provide supplemental thermal insulation around the coolingchamber. At least one of the inner surface of the expandable member orthe outer surface of the cooling chamber may be modified to betopographically non-uniform, so as to provide for a larger interstitialspace volume than in the absence of such modification.

[0015] In another embodiment of the present invention, a cathetercomprises a handle in fluid communication with a supply of cooling fluidhaving a boiling temperature, a source of vacuum, a cooling chamberhaving fluid impermeable inner and outer surfaces, and an elongatecatheter body having a coolant injection lumen having proximal anddistal end portions, the proximal end portion being in fluidcommunication with the supply of cooling fluid, the distal end portionbeing in fluid communication with the cooling chamber. The catheterfurther comprises a primary return lumen having proximal and distal endportions, the proximal end portion being in fluid communication with thesource of vacuum, the distal end portion being in fluid communicationwith the cooling chamber. The catheter also includes an expandablemember having inner and outer surfaces coupled around said coolingchamber, wherein a space exists between the cooling chamber outersurface and the expandable member inner surface. Furthermore, asecondary return lumen is disposed within the catheter body, havingproximal and distal end portions, the proximal end portion being influid communication with the source of vacuum, the distal end portionbeing in fluid communication with the space.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] A more complete understanding of the present invention, and theattendant advantages and features thereof, will be more readilyunderstood by reference to the following detailed description whenconsidered in conjunction with the accompanying drawings wherein:

[0017]FIG. 1 illustrates a balloon catheter system in accordance with afirst embodiment of one aspect of the present invention;

[0018]FIG. 2 shows a cross section taken along the axial directionthrough the balloon portion of another embodiment of the invention;

[0019] FIGS. 3A-3D illustrate four embodiments of thermally conductiveballoons in accordance with the invention;

[0020]FIG. 4 illustrates another embodiment of the invention;

[0021]FIG. 5 illustrates balloon orientation;

[0022]FIG. 6 illustrates an embodiment with proximal anchoring/occlusionballoon;

[0023]FIG. 7 illustrates another two balloon cryocatheter;

[0024]FIG. 7A illustrates a section through a multilumen cathetersuitable for the practice of the invention;

[0025]FIGS. 8A and 8B show another balloon embodiment of the inventionin its deflated and inflated state, respectively;

[0026]FIGS. 9A and 9B show a balloon embodiment with separate coolingand inflation media;

[0027] FIGS. 10A-10B show yet another balloon embodiment;

[0028]FIG. 10C illustrates a further variation on the embodiment ofFIGS. 10A-10B;

[0029]FIG. 11 illustrates another embodiment;

[0030]FIGS. 12A and 12B illustrate delivery embodiments;

[0031]FIG. 13 shows a cross section taken along the axial direction of adual balloon catheter system;

[0032]FIG. 13A illustrates a transverse cross-section of the catheterbody along lines A-A in FIG. 13;

[0033]FIG. 14 illustrates a cross section taken along the axialdirection through the distal portion of the catheter system of FIG. 13;

[0034]FIG. 15 illustrates the catheter system of FIG. 14, when the outerballoon is under vacuum pressure;

[0035]FIGS. 16A, 16B, 16C, 16D, and 16E illustrate various alternativeembodiments of the catheter system of FIG. 14; and

[0036]FIG. 17 shows the catheter system of FIG. 14 with a pressuretransducer located in the inner balloon.

DETAILED DESCRIPTION OF THE INVENTION

[0037]FIG. 1 illustrates a treatment catheter 10 in accordance with abasic embodiment of the present invention. Catheter 10 includes a handle10 a, an elongated intermediate body portion 10 b, and a distal end 10c. An inextensible guide wire 21 extends from the handle to the tip 10 cfor exerting tension via a take up wheel 22 that is turned by lever 24to curve the tip of the catheter and steer it through various branchpoints along the route through a vessel to the intended treatment site.Alternatively, the catheter may be provided with a central guide wirelumen. In that case, a guide wire is inserted into the vessel up to orpast the treatment site and the catheter is then placed over the guidewire. As further shown in FIG. 1, a balloon 30 is attached to the distalend of the catheter and as described further below is in communicationvia the intermediate body 10 b and handle 10 a with an inlet 40 a forthe refrigerant fluid, and an outlet 40 b through which spentrefrigerant returns. The handle may also receive electrical connectionsvia a port or cable 45 for various sensing or control functionsdescribed further below.

[0038] General principles concerning the construction or operation ofsuch a cryocatheter may be found in U.S. Pat. No. 5,281,215 which isincorporated herein by reference for purposes of disclosure andillustration.

[0039] In accordance with one aspect of the present invention, therefrigerant fluid applied at the port 40 a is applied through a firstpassage to the balloon and returned from the balloon through a secondpassage to the outlet 40 b, at a positive pressure. For example, a valvemay be present downstream of the balloon to set a back pressure whicheffects inflation of the balloon by the coolant fluid. As illustrated inFIG. 1, the valve may be implemented by a check valve 51 positioned atthe port 40 b and set for example to open at a pressure of 10 psig tomaintain a sufficient back pressure in the return line for inflation ofthe balloon 30. In alternative embodiments, the check valve 51 may bereplaced by a controllable valve, or a pressure sensing arrangement thatprovides a feedback signal in conjunction with an electricallycontrolled valve, to assure that the desired inflation pressure isachieved at the balloon 30 while allowing return of coolant continuouslythrough the outlet 40 b to a control console. In either case, the returnvalve maintains a minimum pressure at the outlet side of the catheterassembly. This minimum pressure is at a level higher than blood pressureto assure that the balloon inflates and occludes the vessel in which itis located.

[0040] In one embodiment, a relatively thin balloon is placed at the endof the catheter and is folded over the shaft so that when the coolantfluid is injected, the balloon opens and inflates to occlude blood flowwithin the vessel where it is situated. By increasing the injectionpressure to the balloon, the rate of cooling is increased to applycryogenic conditions at the surrounding wall of the vessel. Preferably,a refrigerant such as liquid CO₂ is employed having relativelycontrollable thermal characteristics for the desired treatment range.Leakage of CO₂ into the blood stream, if it occurs, is harmless in smallamounts. This construction may be varied somewhat. For example, theballoon may be a relatively thick-walled balloon intended when inflatedto exert mechanical force against the vessel wall to break up plaque. Inthat case, relatively higher inflation pressures are used, and theoutlet valve 51 may be operated to maintain back pressures up to severalatmospheres or more. Furthermore, it will be understood that therelatively small cross-sectioned opening present in the body 10 d of thecatheter may itself operate to cause a pressure drop, or back pressure,so that the valve 51 may be set to a lower opening pressure threshold,so long as back pressure at the balloon is maintained sufficiently highin the range for balloon inflation.

[0041] In accordance with one aspect of the present invention, theballoon operates to treat adjacent vascular tissue by freezing.

[0042] This is achieved in one preferred aspect of the invention by aballoon fabricated with a wall metallization that enhances the heattransfer rate through all or a portion or pattern of the balloon wall.FIG. 2 is a cross-sectional view through one such balloon 60 taken in aplane along the axis of the device. As shown, the balloon 60 is attachedto the end of the catheter shaft 10 b and has a refrigerant injectiontube 4 extending to its interior so that refrigerant flows out the endor other apertures which are provided in the distal portion of the tube4 and fills a chamber 62 defined by the interior of the balloon. A guidewire lumen 6 may extend to the distal tip for facilitating insertion,and a steering wire (not shown) may be positioned in the adjacentportion of the tip or extend through the balloon, in a manner generallyknown in the art of catheter design to deflect the tip portion. Withinthe body of the catheter shaft 10 b, the region of the lumen notoccupied by the injection tube and other described components serves asa return passage for the refrigerant released from the nozzle end 1 ofthe injection tube 4. As further shown in FIG. 2, the balloon 60 has awall of membrane thickness with a pattern of metallization, visible asmetal regions 64 _(a), 64 _(b) . . . 64 _(c) disposed over its surface.The patterned metallization regions 64 have higher thermal conductivitythan the bulk balloon membrane material, and define regions at whichdestructive freezing contact to the vessel wall itself will occur whenthe balloon is inflated.

[0043]FIGS. 3A through 3D illustrate various patterns suitable for usein the present invention in perspective view on a representative balloon60. As shown in FIG. 3A, one such pattern includes a plurality ofsubstantially axially oriented lines 71 disposed around thecircumference of the balloon. The balloon is shown in a partiallyinflated posture. When inflated more fully, the balloon expands and thelines 71 move apart around the circumference. Since expansion occursonly in the radial direction, the metal does not constrain expansion ofthe balloon or introduce localized stresses or cracking duringexpansion.

[0044]FIG. 3B shows a second useful pattern in which the conductivepattern include a zigzag or meandering arrangement of conductive metalportions 72 configured such that bends or junctions of successive pathregion allow the balloon to expand without constraint. In this case,radial enlargement and circumferential expansion of the balloon wallsimply bends the metal paths. In general, any of the shapes which havebeen found suitable for expanding metal mesh, wire or coil stents may beuseful as surface patterns for the balloon membrane to enable it toundergo radial expansion without introducing mechanical faults into theballoon membrane.

[0045] The invention also contemplates conductive patterns in which theconductive regions consist of a plurality of substantially separated ordisjoint small loci. These may consist of solid regions such as dots 73,or squares or rectangles of relatively small overall extent, e.g., underseveral millimeters across, to produce dimpled regions of conductionextending over the whole surface of the balloon as shown in FIG. 3C, ormay include one or more large areas so as to adapt the balloon forapplying a particular pattern of localized cooling, such as a coolingthrough on side of the balloon while still allowing the balloon toexpand in its entirety to firmly lodge the balloon within the vessel anddisplace blood so as to allow the cooling surface of the balloon toeffectively and directly contact the vessel wall.

[0046]FIG. 3D shows another useful pattern 74 for the balloon.

[0047] The metal or conductive regions 71, 72, 73 and 74 may be appliedusing lithographic printing technology, for example, by applying ametal-loaded thermally conductive ink in a polymer base to the membrane,or by applying complete coatings and patterning and etching away regionsby lithography techniques to form the desired pattern. Such patterns mayalso be formed by applying a metal foil layer or depositing such a layerby plating or sputter deposition techniques and employing lithographicmethods to pattern the continuous layers. In general the pattern isformed so as to create a desired pattern of icing lines for effectivelydestroying tissue at the patterned areas of conductive contact when theballoon is inflated. The conductive regions 64, 71-74 may also becreated by adding thermally conductive materials such as copper powder,flakes or fibers to the material of the balloon membrane itself. In thatcase the powders or fibers are preferably mixed with the appropriateelastomer or polymer material from which the balloon is to be formed,and the balloon is then formed by a known technique such as molding,forming on a mandrel, dipping or other common balloon forming technique.When patterning is desired, a standard elastomer and a conductivelyloaded elastomer may be painted on in bands or otherwise patternedduring the manufacturing process to create the desired thermal contactregions.

[0048]FIG. 4 illustrates another embodiment 80 of the present invention.This embodiment has a multi-balloon structure and a cooling segment 84at the catheter tip. As illustrated, segment 84 corresponds to theexpansion chamber or region of greatest cooling activity of the catheterand includes a cooling pattern assembly. This may be a spiral metalwrapping that provides stiffness, form and thermal conductivity to thesegment. A first balloon 82 is positioned on one side of the coolingsegment 84 to serve as an anchor and blood vessel occluder or flowblocker, and in this embodiment a second balloon 86 extends from theother end of the cooling segment. As shown, the first balloon issubstantially ovaloid and symmetrical, while the second balloon 86 has atapered, trumpet-or bell-shaped aspect that allows it to wedge at theend of a vessel, for example, in the ostium or junction of the vesselend to an organ. Thus, while the balloon 82 is inflatable within avessel to serve as an anchor, balloon 86 is adaptable to fit in anopening and occlude the opening, or define an end-contact geometry forpositioning the cooling segment 84 in close proximity to the vessel endopening.

[0049] It will be appreciated that the cooling segment 84 in thisembodiment has a relatively fixed diameter and is not subject toinflation. Rather it has high thermal conductivity and in use whenactuated by flow of refrigerant within the catheter, an ice ball formsto extend its thermal range. The region of ice formation is indicatedschematically by the external dotted profile positioned around thecooling segment of the catheter.

[0050] As further shown in FIG. 4, the catheter assembly may include aguide wire lumen 87 for over-the-wire insertion, or for monorail guidingmovement of the distal tip. Alternatively, the distal termination mayinclude a conventional wiggler tip or a steering assembly manipulatedfrom the handle end of the catheter. Furthermore, the positions of theballoons 82 and 86 may be interchanged, with the anchor balloon 82 beingpositioned distal to the cooling segment 84 and the tapered or trumpetballoon 86 positioned proximally thereof. This configuration allows useof the catheter by insertion along the opposite direction of the vessel,for example, through a cardiac chamber and into a vessel exiting thechamber.

[0051] Thus, in accordance with this aspect of the invention, thecryocatheter includes a cooling segment that is positioned and anchoredby one or more occlusion balloons. Preferably at least one of theseballoons is inflated with the carbon dioxide or other biocompatiblerefrigerant from the cooling segment. The balloons are not necessarilyof equivalent dimension, geometry or compliance. The anchoring balloonmay be inflated via an individual inflation lumen, thus allowing theposition to be precisely set and this balloon inflated before cooling isinitiated. The tapered balloon may be inflated in multiple waysdepending on the desired effect. For example, when it is desired totreat a lesion in a vessel in close proximity to the ostium, forexample, in the renal arteries, the catheter may be configured such thatthe coolant both inflates and cools the balloon 86, so that its taperedsurface is a contact cooling surface for treating the adjacent vesseltissue.

[0052] In another embodiment, an individual inflation lumen may beprovided for the flared balloon 86. In that case, this balloon may beinflated first when it is desired, for example, to place the coolingsegment 84 in close proximity to the ostium. Balloon 86 may then servethe function both of positioning the cooling segment, and of occludingblood flow in the treated region. Thus, the catheter of FIG. 4 may beused for cryogenic treatment in a blood vessel and is well adapted toforming lesions near or at the ostium of the vessel. As noted above, byreversing the positions of balloons 82 and 86, the catheter may benavigated from the opposite direction along a vessel to treat a sitenear a junction. Furthermore, by reversing the taper orientation of theballoon 86, the catheter may be configured to more effectively treat ajunction of particular size and accessible from one orientation.

[0053] In yet another embodiment, the catheter is manufactured withoutthe symmetric anchoring balloon 82 and carries only the cooling segment84 and trumpet balloon 86 at its tip, forming a configuration for makingrelatively linear lesions in locations where the vessel diameter changesrapidly. For example, such a modified catheter may be used for treatmentin an antegrade approach to a treatment site along the femoral artery,as shown in FIG. 5.

[0054]FIG. 6 shows another embodiment of the invention. This embodimentis similar to that of FIG. 1, but the catheter tip is configured so thatrather than applying cryogenic cooling through an expandable balloon,the cooling segment is of substantially fixed diameter, which may becomparable to that of the catheter body, and it extends distally from aproximal balloon which functions to occlude the blood vessel in whichthe catheter lies. As shown, the tip portion is deflectable by means ofa tension wire connected to the handle, so as to more effectivelynavigate along vascular branching passages. The tension wire may also beoperated to urge the cooling segment into contact at the intended targetsite. As in the embodiment of FIG. 1, the coolant is preferably liquidcarbon dioxide, and the coolant return line is kept at a pressure higherthan the nominal blood pressure in the vessel being treated. The balloonmay thus communicate with the return flow of gas so that the returningcoolant inflates the balloon and effectively occludes the vessel. Byplacing the balloon sufficiently far downstream from the cooling segmentor liquid expansion opening, the return gas may be warmed sufficientlyto avoid freezing tissue in the balloon occlusion region. Similarly, bylocating the balloon closer to the freezing segment, the cooler carbondioxide will provide cryogenic treatment through the balloon surface toan additional region of tissue adjacent the cooling segment. In furtherembodiments, a distal balloon (not shown) may also be provided. Alimiting orifice is preferably placed in the catheter lumen between thecoolant injection tube and the distal balloon to prevent cold gas fromentering the balloon too rapidly. Thus, the distal balloon istrickle-filled from the expansion region of the catheter to providedependable occlusion or anchoring without damaging surrounding tissue.

[0055] In any of the foregoing embodiments, applicant contemplates thata valve release, or an actively-switched vacuum connection may beprovided to quickly deflate the balloons on demand by reducing backpressure of the return lumen in the catheter body.

[0056]FIG. 7 shows another embodiment 90 of the invention, illustratedby way of an axial cross-section taken in a diametral plane through thetip of the catheter. As shown, the tip of the catheter includes a pairof balloons 92 a, 92 b surrounding a cooling segment 93. As shown, thecooling segment and balloons may be formed by a common cylindricalmembrane surrounding the catheter body, while the elongated catheterbody provides necessary lead in and return passages for inflation of theballoons and delivery of cooling fluid. The cooling segment possesses aheat exchanging surface 93 a which may also be a metallic or structuralcomponent of the device. For example, the surface indicated by elements93 a in the Figure may be formed by a metal spring surrounding the body,or by a metal coating or foil lithographically etched to form a coilembedded in or surrounding the membrane. Alternatively, or in addition,the cooling segment may be implemented by a helically slotted coolantsupply tube fixed in the lumen of the catheter shaft to preferentiallydirect the coolant in liquid form against the wall of the coolantsegment. In this embodiment, the catheter shaft 91 is preferably amultilumen shaft, implemented as shown, for example, in FIG. 7A. Thelumena may include, in addition to a guide wire lumen if one isprovided, a lumen 94 for coolant delivery, a larger return lumen 94 cwhich may surround the delivery lumen, and one or more auxiliary lumens94 a, 94 b. In various embodiments the auxiliary lumens are connectedvia the handle to separately inflate one or more of the balloons 92 a,92 b. Alternatively, when balloon inflation is performed by trickleinflation of gas from the cooling segment 93, an auxiliary lumen may beused for a controllable vacuum passage which is actuated to deflate aballoon. As noted above, inflation of the balloons may be effected bythe spent or warmed phase change coolant gas in its course towards thereturn lumen.

[0057] When balloon inflation is entirely effected by gas from thecooling segment, one or more of the lumena may be used to contain asteering wire or other accessory unrelated to fluid transfer. Thus asillustrated in FIG. 7, the catheter 90 may be configured with a guidewire lumen 95 for navigation within a vessel, or may include a steeringand support wire assembly 98 within the catheter body to aid insertion.The invention also contemplates that, in a manner similar to theembodiments described above, the catheter 90 may be implemented with asingle occlusion balloon, which is preferably placed proximal to thecooling segment for antegrade approaches to lesion treatment.Alternatively, the balloon may be placed distally of the cooling segmentwhen it is desired use the device for treating lesions by a retrogradeapproach. When both occlusion balloons 92 a, 92 b are present, thecooling segment is readily anchored in short, branched or turningpassages by inflating one or both balloons. The balloons may further beof different sizes or may be shaped as discussed above for particularapplications and vessels.

[0058] In addition to the specific embodiments discussed above, in oneaspect of the present invention, the invention include a balloondisposed as an annular chamber or cuff around a cooling assembly. Suchan embodiment is shown in FIGS. 8A and 8B. In accordance with thisaspect of the invention, the catheter 10 carries a coolant injectiontube 1 which extends to a cooling chamber structure 103 that issurrounded by a cooling balloon 112. The cooling chamber structure 103is relatively stiff or even rigid and has substantially fixeddimensions. It may be implemented, for example with a cylinder formed ofhard polymer or metal and having a fixed diameter. Surrounding thecooling chamber cylinder 103 is a balloon 112 shown in its deflatedstate in FIG. 8A and shown fully inflated in FIG. 8B. When the coolingand balloon inflation are carried out by the same medium, the coolingchamber 103 may be implemented with a perforated chamber wall. The useof a substantially rigid chamber 103 allows the coolant flow uponexiting the injection tube to undergo substantially regular conditionsand therefore provides well regulated and predictable coolingcharacteristics. However, the invention also contemplates that theballoon may be inflated with a pressurizing medium other than thatprovided by the refrigerant. In either case the balloon may be formed ofa quite thin membrane, on the order of 0.02 millimeters thickness orless, so that in this case it presents very little impediment to heatconduction.

[0059] In this construction, the balloon serves as a compliance memberto conform to irregular tissue surfaces, and may be used to applypressure to a lumen to enlarge the lumen in a manner similar to thatemployed in coronary angioplasty and fallopian tuboplasty procedures.The balloon may also be operated to occlude blood flow when used in anendovascular catheter for rapid therapy since the inflation portion maybe deployed or deflated substantially instantaneously. The balloonfurther operates to center the cooling chamber within the lumen, thusassuring substantially concentric cooling characteristics for thetreatment. Finally, the balloon serves to anchor the cooling chamber inposition.

[0060] The provision of a fixed dimension cooling chamber surrounded byan annular balloon that is inflated by a separate medium, advantageouslyprovides an enhanced spectrum of operating characteristics. Severalexamples follow illustrating the range of this construction of theinvention.

[0061]FIGS. 9A and 9B schematically illustrate the construction of aguide wire cryocatheter 200 having such a circumferential cushioningballoon 212. This construction may also be applied to cooling othercylindrical tissue structures or body lumens, including organs orstructures such as the fallopian tube, esophagus, biliary duct, ureter,gastrointestinal tract and the bronchus. For each of these differentapplications, the relative diameter of the cooling chamber and thethickness of balloon portion may be varied so as to achieve for examplehigh total cooling with a large cooling chamber and an effective rate ofheat transfer from the surrounding tissue area through a relativelythinner layer of cooling balloon. Notably, the balloon may inflated witha medium such as precooled saline solution having a high rate of thermalconductivity and a high thermal storage capacity, to achieve quickchilling and to maintain a stable thermal set point without having todesign the cooling chamber to bear the full thermal load alone.

[0062] As shown in FIG. 9A, the injection tube 201 enters the expansionchamber 203 and injects refrigerant at high pressure, which then expandsin the chamber and is exhausted through the exhaust lumen 205 whichconstitutes the major portion of the catheter shaft. The balloon 212,shown in its collapsed state in FIG. 9A around the circumference of thecooling chamber, is inflated via a balloon inflation lumen 208.Applicant contemplates that the balloon inflation may be effected by anumber of inflation media, including a gaseous coolant medium from theother (coolant) chamber 203. However, preferably, in this embodiment anincompressible liquid such as saline solution having a high thermalcapacity and excellent heat conductive properties is applied through theinflation tube 208 to fill the balloon as shown in FIG. 9B. The externalsurface of the expansion chamber 203 may be provided with texture, suchas a plurality of isolated bumps or dimples 207, of which several areshown in cross-section, to provide unobstructed fluid percolationpassages along the surface and assure that the balloon inflation fluidmay have free access and flow quickly to and from the passage 208. Thisallows the balloon to fully deflate when fluid is withdrawn via passage208.

[0063] A guide wire lumen 220 passes centrally through the coolingchamber assembly and as shown in FIG. 9B accommodates a guide wire 221for directing and positioning the catheter. As further shown in thoseFigures, the outer diameter of the cooling chamber may extend for arelatively great portion of the total diameter of the device so that theballoon portion occupies only a thin shell which effectively extends thereach of the cooling chamber and provides a short heat conduction pathtogether with firm compliant contact with surrounding tissue. As notedabove, when used for angioplasty and other cryogenic treatment contextsthe balloon serves to apply a stretching or extensile force to tissue,which is conducive to the desired tissue treatment destruction orregeneration process. The provision of such enlarged cooling chamberalso provides a greater external surface area for the coldest centralstructure of the catheter, greatly enhancing the rate of thermaltransfer achieved with the balloon assembly.

[0064] In general the body of the catheter may be comparable to that ofexisting treatment devices, e.g., one to four centimeters in length foran endovascular angioplasty device. However the cryogenic portion neednot extend the full length of the tip assembly, and the structure mayinclude axial extension portions which are not cryogenically cooled.

[0065]FIGS. 10A through 10C illustrate a construction of a cryocatheter300 of this type. In this embodiment, the tip of the catheter includeschambers 303, 303 a and 303 b all located within the balloon. Thechamber 303 serves as a cooling expansion chamber in the mannerdescribed above, and the cooling injection tube 301 opens into thatchamber. At the proximal and distal ends of chamber 303, pair of dummychambers 303 a, 303 b extend continuously with the main body of thechamber to form a single elongated cylindrical structure lying withinthe balloon 312. However, the end chambers 303 a, 303 b are isolatedfrom the injected coolant, and themselves form dummy spaces or uncooledregions that serve simply to provide positioning support. As furthershown in FIG. 10A, the balloon 312 has corresponding segments denoted312 a, 312 b and 312 c that are partitioned from each other such thatthe end segments are separated from the central cooling portion of theballoon. These segments lie over subchambers 303 a, 303 and 303 b. Theymay be serially connected or separately supplied with inflationmaterial, so fluid entering the balloons is cooled only in the centralregion.

[0066] The illustrated embodiment of FIG. 10A has a generally continuousballoon contour in which at least a portion of the end segments 312 a,312 b inflates to the diameter of the surrounding blood vessel or tissuelumen and serves to displace blood, fluid or tissue away from thecryogenic treatment portion at the center of the catheter tip. As shownin FIG. 10B, this has the effect of creating a cooling region that formsa relatively symmetrical ice ball volume (indicated by dashed lines inthe Figure) around the vessel and catheter tip, with greater depth ofpenetration centered directly over the cryogenic chamber and withcooling damage tapering off away from that region. The balloon need notbe a single continuous or partitioned balloon but may be implementedwith separate balloons that in turn may be inflated via separate filleror inflation tubes (not illustrated) so as to more effectively achieveor more independently initiate the blocking and heat isolationfunctions. FIG. 10C illustrates one such embodiment 400, in which acryogenic balloon 412 is surrounded by first and second blocking orblood displacing balloons 412 a, 412 b that are offset a short distanceaway from the ends of the coolant chamber. With this construction theexcluding balloons may be positioned more remotely from the cryogenicsegment.

[0067] In any of the foregoing embodiments, the balloon may beconfigured to apply a chilling level of cold without freezing ordestroying tissue when appropriate for the tissue involved. As with thebasic embodiment shown in FIGS. 8A and 8B, the catheter of the presentinvention preferably allows the withdrawal of sufficient thermal energyform the target site to freeze tissue, while the balloon anchors orenhances the positioning of the cryogenic source within the lumen so asto deploy the resulting ice ball in an appropriate relation to thesurrounding tissue. The balloon enhances control of adjacent blood flowand may be used to arrest blood flow in the vessel entirely so thattherapeutic cold accrues more quickly and is not dissipated. By activelypumping out the inflation fluid, collapse of the balloon followingtherapy allows more immediate resumption of circulation to perfusetissue. Furthermore, by using a liquid-inflated balloon, the device maybe deployed in much the same manner as an existing angioplasty catheter,and the guide wire lumen allows simple navigation and use of the devicewithout requiring that the physician or cardiology specialist acquireadditional operating skills or specialized training.

[0068] The catheter shaft may accommodate various lumens either as partof the shaft extrusion, or by carrying them as separate tubes such as aninjection tube, a coolant exhaust lumen, a balloon inflation lumen, aguide wire lumen and other lumens, for example, for carrying wires toheating elements and/or monitoring devices to sense pressure,temperature and other sensing functions. By making the diameter of thecryogenic chamber large in relation to the targeted tissue lumen, theballoon may be formed with a low interior volume, facilitating thethawing of the inflation medium and reducing the time of total vascularobstruction. The thawing may further be advanced by providing andactivating one or more heating elements, which may include any of a widevariety of heating means within the catheter body, such as resistiveheating, radio frequency heating, laser heating applied via an opticalfiber extending through the catheter body, microwave heating or heatedgas or liquid infusion applied to the balloon portion. These may alsoinclude, in various treatment regimens, sources of energy that areexternally applied to a catheter designed to preferentially receive suchenergy. Such external heating energy sources may, for example, beultrasound or electromagnetic radiation applicators. The heater may alsoinclude various semiconductor, thin layer resistive or other similartechnologies deployed, for example, on the balloon surface so as to heatone or more of the wall of the body lumen, the balloon inflation medium,or various pieces of the catheter structure.

[0069] In addition, the period of blood flow obstruction may be furtherreduced by providing a structure as shown in FIG. 11. In this case, thecatheter 500 includes perfusion channels 531, 532 that extend throughthe catheter structure to allow blood to flow along the tissue lumenduring the balloon inflation time interval and before extreme coolinghas occurred to freeze off the central region. In this embodiment, theballoon may be inflated to securely position and center the assemblywhile blood continues to flow along the vessel. Cooling is then started.While the bypass channels 531, 532 may be expected to freeze off oncethe cooling injection has started, the invention also contemplates thatthe bypass channels may be insulated from the cooling chamber, or theymay include resistive or other heating elements to maintain theirtemperature suitable for continued blood flow during cryoablation. Suchbypass passages may also be positioned in part in or through thecatheter shaft or guide wire lumen.

[0070] The invention also contemplates a catheter as described abovecombined with other known catheter subassemblies or accessory devicessuch as drug delivery, energy delivery or stent delivery elements, orstructures for delivering radiation. In other embodiments the cathetermay include one or more additional balloons such as a primaryangioplasty balloon in addition to the blocking balloons and thecryotreatment balloon described above. In yet other embodiments of theinvention, the catheter may include a supply tube for ejecting abioactive or simply thermally conductive material in the spacesurrounding the cooling portion, to form a temporary frozen plug whichmay be left in place following withdrawal of the catheter.

[0071]FIGS. 12A and 12B illustrate two such delivery catheters 600, 700.As shown in FIG. 12A, a first delivery catheter 600 includes anelongated body and cryogenic tip 610 with a cooling chamber 603 fed by acoolant injection lumen 601 as described above. Catheter 600 furthercarries a stent 620 on its outer surface and is configured to deliverand install the stent at an endoluminal site. By way of example thestent 620 is illustrated as having ends 621, 622 contoured to retain thestent on the catheter during delivery, but other retention means, suchas a removable or telescoping retaining sheath may be employed. Thestent is made of a shape-memory alloy or other biphasictemperature-dependent material that changes its shape when brought topredetermined temperature. For operation, the catheter tip is deployedto a desired site and then operated to bring about atemperature-dependent change in shape or dimension of the stent 620.This may be accomplished before, during, after, or independently of, thecryogenic treatment of nearby tissue. Depending on the particular alloyemployed in stent 620, the fixation in position and shape change may beeffected by applying cryogenic temperature, or else a mild amount ofcooling may be applied to cause the stent to retain a compact shapeduring insertion and the stent may subsequently deploy as thesurrounding temperature rises to normal body temperature. It will beunderstood that in general the alloy properties of such materials may beadjusted so that a relatively large change in shape or conformation isachieved at one temperature threshold, which may be above or below bodytemperature. Accordingly, for this aspect of the invention, applicantcontemplates the possibility of providing a heater as well as thecryochamber 603 to provide both hypo- and hyperthermal conditions tocarry out stent deployment.

[0072]FIG. 12B illustrates another embodiment 700 of a cryogenicdelivery catheter of the invention. This embodiment again has the basicstructure of a cooling chamber 703 in a distal cooling tip 710 fed by acoolant supply lumen 701. However, in this embodiment an additionalfluid delivery line 725 extends through the catheter body and is mountedto deliver fluid F externally of the tip 710 into the space between thecooling chamber exterior wall and the surrounding tissue. The deliveryline 725 may have one or more outlets positioned to provide fluid F indefined locations. As illustrated in phantom by element 715, aperforated membrane or other external distribution structure may also beprovided to disperse or spread the fluid F exiting the delivery line725. In general, the delivery line 725 may deliver a therapeutictreatment liquid, or simply a heat conduction fluid to cryochambersurface. Applicant contemplates generally that during cryotreatment, thefluid F will freeze in place, forming a plug that blocks flow, conductsthermal energy, and otherwise cooperates with the cryotreatmentoperation as described above. Advantageously, however, upon (or evenprior to) completion of the freezing treatment, the catheter 700 may bewithdrawn while leaving the frozen fluid mass in place. This mass thencontinues to chill the lumenal tissue wall, while (in the case of avessel) circulation is immediately restored through the center. Thus,the duration of catheter freezing operation or the duration of bloodflow occlusion may each be reduced, offering significant clinicaladvantages.

[0073]FIG. 13 illustrates yet another embodiment of the presentinvention, a dual balloon catheter system labeled generally as 800.Catheter system 800 includes a catheter 805, a handle unit 810, aguidewire port 815, a guidewire tube 820 enclosing a guidewire lumen822, a coolant port 825, a coolant injection tube 830 enclosing acoolant injection lumen 835, a vacuum port 840, a vacuum return tube845, a primary vacuum return lumen 850, a secondary vacuum return lumen855, an inner balloon 860, an outer balloon 865, a cooling chamber 870,a proximal thermocouple 875, a distal thermocouple 880, and a distal tip883. The thermocouples may also be coupled to a temperature gauge 885coupled to handle unit 810.

[0074] The catheter 805 includes an elongate tube or series of tubes,conduits, flexible or rigid members generally suited for the flow ofcoolant therein, and for the insertion of such catheter into narrow bodylumens such as blood vessels. Each of these tubes, conduits or membersmay include a number of lumens. As used herein, the term lumen refersnot merely to the bore of a tube, but refers generally to a definedfluid pathway, suitable for the flow of coolant therethrough, connectingtwo or more spaces or elements such that the spaces or elements are influid communication. The catheter 805 is constructed similar to thoseembodiments previously discussed herein, and operates in a similarfashion so as to enable cryotreatment of tissue.

[0075] As shown in FIG. 13, the catheter 805 is coupled to a handle unit810 at its proximal end, and both of balloons 860 and 865 at its distalend. The handle unit 810 is fitted with multiple ports, including aguidewire port 815 for the insertion of a guidewire (not shown) intoguidewire tube 820. In addition, the handle unit 810 includes a coolantport 825 for the injection of coolant from a coolant supply (not shown)into coolant injection lumen 835. The coolant injection lumen 835 isdisposed between the coaxial coolant injection tube 830 disposed aroundguidewire tube 820, as illustrated in FIG. 13.

[0076] A vacuum port 840 is also coupled to the handle unit 810, suchport being coupled to a suitable vacuum generating device. A vacuumreturn tube 845 is disposed coaxially around the coolant injection tube830 and inside of the catheter tube 805. This creates two separatecoaxial vacuum return lumens: a primary vacuum return lumen 850 disposedbetween coolant injection tube 830 and vacuum return tube 845, and asecondary vacuum return lumen 855 disposed between the vacuum returntube 845 and the catheter body 805.

[0077]FIG. 13A illustrates a cross-section taken in the transversedirection of the catheter 805, along lines A-A in FIG. 13, showing thecoaxial arrangement of the various tubes and lumens discussed above.

[0078] Turning back to FIG. 13, the catheter 805 is coupled at itsdistal end to two balloons, inner balloon 860, and outer balloon 865.Each of these balloons include materials and are constructed in a mannersimilar to those balloons discussed in previous embodiments. The innerballoon 860 has an open proximal end coupled to the coaxial return tube845, and may have its lateral outer surface adhesively coupled to theguidewire tube 820. The outer balloon 865 is disposed around the innerballoon 860, having its proximal end coupled to the catheter tube 805and its distal end coupled to the distal tip 883 disposed around thedistal end portion of the guidewire lumen 822.

[0079] High pressure coolant is injected through the coolant port 825into the coolant injection lumen 835, whereby it flows through suchlumen to be injected into the inner balloon 860. The inner balloon 860thereby expands to create a cooling chamber 870 therein. The coolantthen flows out of the cooling chamber 870 into the primary vacuum returnlumen 850, and eventually out of the device through the vacuum port 840.For purposes of this invention, a “vacuum” is merely the effect of fluidevacuation, wherein static pressure in a space may be below that ofatmospheric, or may be below the static pressure in the flow regionimmediately “upstream” of such space. Therefore, a “vacuum”, as usedherein, may refer simply to the existence of a negative pressuregradient in a flow region. Thus, the flow of coolant from the coolingchamber 870 through the primary vacuum return lumen 850 is driven by thenegative pressure gradient created when the pressure therein is lowerthan the static pressure of coolant in the chamber 870.

[0080] While the coolant is flowing through the chamber 870, twothermocouples disposed therein may take temperature readings of thecoolant, such temperature being measured by the temperature gauge 885.While the proximal thermocouple 875 takes a temperature reading in theproximal section of the cooling chamber 870, a distal thermocouple 880takes a reading of coolant temperature in the distal section of coolingchamber 870. As coolant is injected into the inner balloon 860, the flowof coolant in such balloon is non-uniform, unsteady, and turbulent, suchthat a uniform temperature profile for cryotreatment is not achieved fora finite time. The thermocouples 875 and 880 provide for feedbackcontrol of the flow of coolant, and of the resultant temperature profileachieved in chamber 870, thereby enabling more efficient cryotreatment.

[0081]FIG. 14 illustrates the distal end portion of the catheter system800 of FIG. 13. In addition to the elements displayed in FIG. 13, FIG.14 illustrates a coaxial coolant injection orifice 905, an interstitial,“intra-balloon” space 910 disposed between inner balloon 860 and outerballoon 865, and coolant flow lines F. Upon flowing through the coaxialinjection tube 830, coolant enters the chamber 870 through the injectionorifice 905 located in the distal half of inner balloon 860. Coolantthereafter generally flows in the direction F until the inner balloon860 is inflated to form the cooling chamber 870 in substantially theshape and form shown in FIG. 14. Coolant then flows out of the chamber870 through the primary vacuum return lumen 850.

[0082] While coolant is contained in the chamber 870, the flow thereinis regulated by the use of thermocouples 875 and 880, so as to controlthe temperature profile therein. The pressure conditions inside of thechamber 870 may be regulated by controllably injecting the coolantthrough the orifice 905, such that the desired mixture of liquid and gasphase coolant is evaporated and expanded, respectively, inside thechamber to achieve the desired cooling power. The injected coolant maybe (i) substantially in gas phase immediately upon injection, therebyusing mainly Joule-Thomson cooling to lower the temperature profile inthe chamber 870, or, (ii) substantially in liquid form, allowing forbetter control of temperature across the length of chamber 870, whilestill providing cooling through the endothermic boiling of liquid phasecoolant.

[0083] In either case, the pressure inside of the chamber 870 must bemaintained at safe levels for insertion of the device into the humanbody. Generally, the static pressure of coolant inside of the chamber870 must be maintained below 15 psia, or only slightly above the ambientpressure outside of the device. If a leak or rupture through the innerballoon 860 develops, the vacuum applied through the secondary vacuumreturn lumen 855 will act to siphon any leaking coolant from space 910into the vacuum return lumen 855. In this sense, the dual balloonconfiguration is robust with respect to balloon integrity failure, inthat the failure of one balloon 860 is contained by the presence ofanother outer balloon 865.

[0084] Furthermore, the presence of the space 910 provides additionalthermal insulation which may be necessary when operating the device atrelatively low pressure inside of chamber 870. Empirical evidence showsthat at chamber static pressures of 15 psia, the cooling power of thecoolant flow expanding in the chamber 870 may at times be too high forsafe and effective cryotreatment of adjacent tissue. In order to operateat such pressures, additional thermal resistance is needed around theinner balloon 860 to mitigate the excessive cooling power of the device.The space 910 effectively provides such insulation, which may befine-tuned by applying varying levels of vacuum through the return lumen855. In such a manner, the effective temperature applied duringcryotreatment of tissue may be warmer than that of the boilingtemperature of the coolant.

[0085] However, FIG. 14 illustrates the disposition of the outer balloon865 around the inner balloon 860 such that an interstitial envelope orspace 910 exists therebetween, when inner balloon 860 is inflated to apressure higher than that present in the secondary vacuum return lumen855 and hence inside of the space 910. This may be the case prior to thecreation of vacuum pressure inside of the space 910, as applied throughthe secondary vacuum return lumen 855. However, once vacuum pressure isapplied into the space 910, the balloon configuration is that shown inFIG. 15. Under such conditions, the space 910 is effectively of zerodimension along the lateral faces L of both balloons, such that theinner balloon 860 and the outer balloon 865 are in contact with oneanother along length L.

[0086] If the space 910 is thereby closed, the containment andinsulating functions of the device are decreased. To counteract this,various methods and devices may be used to maintain the space 910 so asto enable vacuum containment of coolant leaks from, and provideadditional thermal resistance around, the chamber 870, while preventingthe two balloons 860 and 865 from sealing in and apposing againsteachother as shown in FIG. 15. The balloons 860 and 865 may still remainin apposition versus one another, but the space 910 will be maintainedto achieve one of the purposes and functions of the present invention,as more specifically explained below.

[0087] One such embodiment is shown in FIG. 16A, where the outer surfaceof inner balloon 860 is modified to create small surface patterns thatextend from the outer surface as shown. As used herein, the term“surface modification” shall mean the creation or use of elements whosesurfaces are topographically non-uniform, i.e. non-smooth. The slope atany point on such a surface may be continuous or non-continuous, but thesurface itself will be continuous. These surface modifications 1010 maybe achieved through conventional plasma treatment, vapor deposition, orthrough the use of electrically conductive or radiopaque materials as isknown in the art, and may be patterned or non-patterned, so as to allowfor more effective fluid pathways through the space 910. Such surfacemodification thereby effectively maintains the space 910 at a finitelevel while vacuum is applied through the return lumen 855.

[0088] Other configurations which maintain the space 910 are shown inFIGS. 16B through 16E. FIG. 16B shows the use of small particles 1020,such as talcum powder, to be lodged in the space 910. Alternatively, thespace 910 could be filled with a fluid, which may itself be radiopaqueor electrically conductive. In either case, the use of a vacuum returnlumen coupled to the outer balloon 865 is not needed, and the outerballoon 865 is sealed to the coaxial vacuum return tube 845 which alsoserves as the outermost tube of the catheter shaft. This allows theparticles 1020, or fluid if fluid is used, to be sealed and contained inthe space 1020 during operation of the device. Alternatively, a vacuumreturn tube such as is used in previous discussed embodiments may becoupled to the proximal end of balloon 865 and coupled with a separateinjection mechanism (not shown) for maintaining the steady flow andpresence of particles 1020, or fluid, as needed, so as to maintain space910 in its desired dimension.

[0089]FIG. 16C shows the use of regular or irregularly patterned surfaceridges 1030 coupled to either of: (i) the outer surface of inner balloon860, or (ii) the inner surface of outer balloon 865. Another alternativeto maintain space 910 is to use a braid or mesh type structure 1040 asshown in FIG. 16D, wherein the mesh 1040 surrounds the outer surface ofthe inner balloon 860. The cross-sectional thickness of the mesh 1040provides for the thickness of the space 910. The mesh 1040 may be abraid formed by a first group of flexible elongate elements 1042helically wound in a first direction of rotation and a second group offlexible elements 1044 helically wound in a second direction of rotationto create a braid as shown in FIG. 16D. The space 910 is thus maintainedby the apposition of each of the inner balloon 860 and the outer balloon865 against the mesh 1040, wherein each flexible elongate element has acircular cross section defined by a diameter. In an exemplaryembodiment, this diameter is in a range of approximately 0.001 to 0.010inches. The flexible elongate elements 1042 and 1044 may be formed ofmetal, or a filament or fiber such as nylon, aramid, or polyester.

[0090] Finally, another embodiment uses a coil 1050 as shown in FIG.16E. Either of the coil or mesh may be made of metal, nylon, polyimideor other suitable material, as is known in the art. The coil 1050 mayinclude a single element wound in a direction around the inner balloon860, or may be formed by a number of such elements wound in a parallelrotational direction so as to form a coil or spring. Each such coilelement 1050 has a circular cross section defined by a diameter,wherein, in an exemplary embodiment, the diameter is in a range ofapproximately 0.001 to 0.010 inches. Alternatively, the coil element1050 may have a rectangular cross section defined by a height vs. awidth, wherein, in an exemplary embodiment, the height is in a range ofapproximately 0.001 to 0.010 inches, and the width is in a range ofapproximately 0.001 to 0.010 inches. The coil element 1050 may be formedof metal, or a filament or fiber such as nylon, aramid, or polyester.

[0091] The pressure conditions inside of the chamber 870 may also bemonitored and regulated through the use of a pressure transducer 1060located inside of the chamber 870, as shown in FIG. 17. The pressuretransducer 1060 gives a user feedback control of the flow and pressureinside of the inner balloon 860 as the balloon is inflated and thecatheter device is inserted and operated inside of a body lumen.Furthermore, the primary vacuum return lumen 850 may be set with a backpressure effective for inflating the cooling chamber 870 with thecooling fluid such that the cooling chamber 870 expands within a bodylumen or vessel to position the device proximate to the vessel wall forperforming cryotreatment. The back pressure is set to adjust the boilingtemperature of the coolant and thereby determine the temperature appliedto the surrounding tissue for cryotreatment. Such back pressure may bemonitored and controlled by means of additional pressure transducers(not shown) in the catheter body. Furthermore, such a back pressure maybe created by restricting the coolant return path through primary vacuumreturn lumen 850. Such restriction may be created by selecting adiameter of either of the injection tube 830, or coaxial return tube845, such that the coolant flow generates a residual pressure.Alternatively, the pressure conditions, including the chamber 870pressure and the back pressure in return lumen 850, may be regulated bythe control of the coolant fluid flow rates.

[0092] It will be appreciated by persons skilled in the art that thepresent invention is not limited to what has been particularly shown anddescribed herein above. In addition, unless mention was made above tothe contrary, it should be noted that all of the accompanying drawingsare not to scale. A variety of modifications and variations are possiblein light of the above teachings without departing from the scope andspirit of the invention, which is limited only by the following claims.

What is claimed is:
 1. A catheter comprising: an elongate catheter body,a cooling chamber defined within the catheter body, an expandable memberdisposed around the cooling chamber.
 2. The catheter of claim 1, whereinthe expandable member envelops the cooling chamber.
 3. The catheter ofclaim 1, wherein the expandable member is disposed around the coolingchamber to define an interstitial space therebetween.
 4. The catheter ofclaim 3, wherein the interstitial space is in fluid communication with asource of fluid evacuation.
 5. The catheter of claim 3, wherein thecooling chamber is a first expandable membrane inflatable from a firststate to a second state.
 6. The catheter of claim 5, wherein thecatheter body further comprises a coolant injection tube in fluidcommunication with: (i) a source of coolant, and (ii) the coolingchamber, and wherein the cooling chamber is inflatable by the flow ofcoolant from the injection tube into the first expandable membrane. 7.The catheter of claim 6, wherein the catheter body further comprises aprimary coolant return lumen in fluid communication with: (i) a sourceof fluid evacuation, and (ii) the cooling chamber, and wherein thecoolant injection tube, the cooling chamber, and the primary coolantreturn lumen define a first fluid pathway for the flow of coolant. 8.The catheter of claim 7, wherein the catheter body further comprises asecondary coolant return lumen in fluid communication with: (i) a sourceof fluid evacuation, and (ii) the interstitial space, and wherein theinterstitial space and the secondary coolant return lumen define asecond fluid pathway for the flow of coolant.
 9. The catheter of claim3, wherein the cooling chamber has an outer surface and the expandablemember has an inner surface, said surfaces being substantially inapposition to one another to define a first volume of the interstitialspace.
 10. The catheter of claim 9, wherein at least one of (i) theinner surface of the expandable member, and (ii) the outer surface ofthe cooling chamber, is topographically non-uniform.
 11. The catheter ofclaim 10, wherein at least one of (i) the inner surface of theexpandable member, and (ii) the outer surface of the cooling chamber, ispatterned to enhance the flow capacity of fluid flow in the interstitialspace.
 12. The catheter of claim 10, wherein at least one of (i) theinner surface of the expandable member, and (ii) the outer surface ofthe cooling chamber, is in part formed using plasma treatment.
 13. Thecatheter of claim 10, wherein at least one of (i) the inner surface ofthe expandable member, and (ii) the outer surface of the coolingchamber, is in part formed using vapor deposition of additional materialonto said surface.
 14. The catheter of claim 10, wherein at least one of(i) the inner surface of the expandable member, and (ii) the outersurface of the cooling chamber, is in part comprised of a plurality ofpartially raised surfaces arranged on said surface.
 15. The catheter ofclaim 8, further comprising a plurality of small particles disposed inthe interstitial space.
 16. The catheter of claim 3, further comprisinga flexible structure disposed within the interstitial space and aroundthe cooling chamber.
 17. The catheter of claim 16, wherein the flexiblestructure comprises at least one flexible elongate element wound in afirst direction of rotation around the cooling chamber.
 18. The catheterof claim 16, wherein the flexible structure further comprises at leastone flexible elongate element wound in a second direction of rotationaround the cooling chamber.
 19. The catheter of claim 17, wherein theflexible elongate structure has a cross-sectional thickness in the rangeof 0.001 to 0.01 inches.
 20. The catheter of claim 1, further comprisingat least one temperature sensor disposed within the cooling chamber. 21.The catheter of claim 1, further comprising at least one pressure sensordisposed with the cooling chamber.
 22. A catheter comprising: a handlein fluid communication with a supply of cooling fluid having a boilingtemperature, and a source of fluid evacuation, a cooling chamber havingfluid impermeable inner and outer surfaces, an elongate catheter bodyhaving a coolant injection lumen having proximal and distal endportions, the proximal end portion being in fluid communication with thesupply of cooling fluid, the distal end portion being in fluidcommunication with the cooling chamber, and a primary return lumenhaving proximal and distal end portions, the proximal end portion beingin fluid communication with the source of vacuum, the distal end portionbeing in fluid communication with the cooling chamber, an expandablemember having inner and outer surfaces coupled around said coolingchamber, wherein a space exists between the cooling chamber outersurface and the expandable member inner surface, and a secondary returnlumen disposed within the catheter body, having proximal and distal endportions, the proximal end portion being in fluid communication with thesource of vacuum, the distal end portion being in fluid communicationwith the space.
 23. The catheter of claim 22, wherein the coolingchamber is controllably filled with cooling fluid, and vacuum is appliedto the primary return lumen to direct the cooling fluid to flow from thecooling chamber through to the primary return lumen.
 24. The catheter ofclaim 23, wherein the outer surface of the expandable member is disposedin contact with tissue proximate a body lumen to effect thermalconduction between said tissue and the flow of cooling fluid in thecooling chamber.
 25. The catheter of claim 23, wherein vacuum is appliedto the secondary return lumen.
 26. The catheter of claim 22, wherein thecooling chamber is an inflatable membrane transitionable from a firstvolume to a second volume, the second volume being larger than the firstvolume.